Project Summary The overall goal of Project 4 is to determine how the nociceptin/receptor system modulates the mesolimbic dopamine (DA) system and behavioral responses associated with stress, aversion, and motivated behaviors. We recently identified a population of paranigral ventral tegmental area (pnVTA) nociceptin (PNOC+) neurons that constrain motivated behavior and regulate the motivation for natural reward seeking. These PNOC+ pnVTA neurons are engaged during motivation, as well as carry a negative valence when activated. Our extensive body of preliminary findings strongly implicate these neurons in regulating motivated behaviors, stress responsivity, and avoidance behavior. Working in close collaboration with the other Projects (in particular, Projects 1 and 3), Project 4 will use newly developed mouse model for accessing endogenous nociception circuits and focus on the neurobiological mechanisms of how the prepronociceptin system engages the dopamine system to regulate motivation ? a key component of depressive disorders, including those outlined in this center project. The research aims of this 5-year project are: (1) to determine the anatomical and functional characteristics of nociceptin expressing neurons within the ventral midbrain and identify behavioral conditions (acute vs chronic stress, motivation and Approach-Avoidance) that are modulated by this system; (2) to identify and characterize pnVTA nociceptin neurons and their afferents involved in motivated behavior that drive negative affective behavior. The project will use novel and validated mouse cre-driver models that allow unparalleled access to PNOC+ neurons in the VTA, combined with optogenetic, chemogenetic, calcium imaging, viral tracing, and behavior to uncover circuit mechanisms that underlie how these neurons are regulated by aversive stimuli. This project directly synergizes with the other projects outlined in this Conte Center, in two key ways: 1) using novel cutting-edge mouse models, it will allow to dissect the role of prepronociceptin system in motivation, and 2) it will comprehensively examine the role of nociceptin circuits in dopamine-dependent behaviors, with direct relevance to motivational states, avoidance, and stress-induced negative affect. Results from Project 4 will: (1) directly inform post-mortem analyses probing nociception neurons in the pnVTA of individuals with MDD who died by suicide (Project 1); (2) synergize with pharmacological challenges used to test the hypothesis that nociceptin receptor antagonism will normalize neural substrates underlying approach/avoidance behaviors in humans with MDD and anxiety disorders (Project 1); and (3) integrate with studies using PNOC-IRES-cre mice to determine how specific populations of nociceptin neurons (striatal vs VTA) regulate motivation, anhedonia, and approach/avoidance decision making (Project 3). Data emerging from Project 4?s aims, together with the three other projects and the Computational Modeling Core will fundamentally enhance our understanding of the nociceptin/NOPR system in motivation and depressive/anxious behaviors, and identify novel treatment targets.